Your MAG58 (M240 for us) is a supressive fire weapon. Prone is the most effective position for all shoulder arms. The MAG isn't supposed to be used for room clearing, it's to support the rest of your platoon with a wall of lead.

"I have always been a soldier. I have known no other life. The calling of arms, I have followed from boyhood. I have never sought another." From The Virtues of War, by Steven Pressfield.